isnull vs is null

Question

I have noticed a number of queries at work and on SO are using limitations in the form:

isnull(name,\'\') <> \'\'

Is there a particul

Answer 1

Others have pointed out the functional difference. As to the performance issue, in Postgres I've found that -- oh, I should mention that Postgres has a function "coalesce" that is the equivalent of the "isnull" found in some other SQL dialects -- but in Postgres, saying

where coalesce(foobar,'')=''

is significantly faster than

where foobar is null or foobar=''

Also, it can be awesomely dramatically faster to say

 where foobar>''

over

where foobar!=''

A greater than test can use the index and thus skip over all the blanks, while a not-equal test has to do a full file read. (Assuming you have an index on the field and no other index is used in preference.)